1. Field of the Invention
The present invention relates to a signal transmission system and a vehicular lamp.
2. Description of Related Art
In late years, a vehicular lamp that uses a semiconductor light-emitting element such as an LED (Light Emitting Diode) for a light source is known as disclosed, for example, in Japanese Patent Laid-Open No. 2002-231013 (see pages 2 to 6 and FIGS. 1 to 13). For safety reasons, when a light source of a vehicular lamp breaks, the vehicle informs a driver of that effect and prompts the driver for replacement of the light source. In addition, when the speed of a vehicle is fast, the vehicle increases a light amount of the light source more than it drives slowly. In this way, the front of the vehicle becomes brighter and safety of vehicle traveling is increased, in some cases.
In order to detect disconnection of a light source by a vehicle main body, a signal line, which transmits a signal to indicate disconnection of the light source from a vehicular lamp to the vehicle main body, is required. In addition, when a light amount of the light source is controlled, a signal line, which transmits a control signal from the vehicle main body to the vehicular lamp, is required. Therefore, since the number of cables connected to the vehicular lamp increases, there has been a problem that the vehicular lamp is not miniaturized in some cases. In addition, due to an increase of the number of cables, there has been a problem that it takes a long time to mount the vehicular lamp to the vehicle in some cases.